Prior art processes for ABS polyblends have generally grafted diene rubber particles contained in aqueous emulsion with alkenyl aromatic and alkenyl nitrile monomers to form grafted rubber phase particles dispersed in a matrix phase of said monomers.
The rubber particle size in such rubber emulsions ranges generally from about 0.01 to 0.50 microns which will toughen the matrix phase if incorporated in relatively high concentrations, i.e., 10 to 25% by weight.
The surface gloss of such polyblends is high, as extruded into profiles or molded into articles, because the particle size is too small to disturb the surfaces of the article.
U.S. Pat. No. 3,509,237 discloses that the toughness of ABS polyblends can be improved by adding large particles of grafted rubber, i.e., in the range of about 1 to 2.5 microns to ABS polyblends having rubber particles ranging from 0.01 to 0.50 microns.
It was noted that the large particles lowered gloss and no more than about 3 to 30% of large particles could be used to improve toughness and yet maintain reasonable gloss. Gloss as measured by the well known Hunter Gloss Test could be reduced from about 90 to about 60 using up to about 50% large particles.
Recent commercial requirements for extruded sheet material in formed articles such as housings for appliances, luggage and automotive require that the polyblend have lower gloss to provide a deeper color appearance to formed articles.
The use of larger rubber particles, as disclosed above, is not feasible because gloss cannot be lowered to gloss levels of about 10 to 20 without using all large rubber particles which lowers possible rubber concentrations and toughness.
The bimodal particle size systems of small and large particles then cannot be used to optimize low gloss. These systems also present the problem of preparing two different grafted rubber particle sizes and blending as a separate batch operation increasing costs and lower efficiencies of production.
It has now been discovered that small rubber particles can be grafted with alkenyl aromatic and alkenyl nitrile monomers formulations containing 1 to 15% by weight of conjugated diolefin monomers while forming terpolymers of said monomers having said grafted rubber particles dispersed therein and also a macrogel fraction of larger particles having a largest dimension greater than 1 micron and ranging from 1 to 50 microns or larger preferably 5 to 20 microns. The large particles as observed in electron micro photographs appear as crosslinked or associated masses (gels) of rubber particles and terpolymers or macrogel particles as contrasted to the individual rubber particles which are crosslinked small microgels and appear as individual particles.
The diolefin monomer provides the graft terpolymer and the matrix terpolymer with residual unsaturation that leads to crosslinking at least a portion of the matrix polymer and the grafted rubber into gel fractions in the polyblend that become dispersed as domains of macrogel or large gels which lower the gloss of the formed polyblend article.